Not My Brother’s Keeper: The Strange Consequences Of Sibling Rivalry In The Womb

As the 5th of 8 children, sibling rivalry was an inescapable fact of life. Jockeying for parental attention and investment can sow seeds of distrust and animosity between brothers and sisters, not to mention jealousy and anger. Of course, not all large families were like mine. I’m sure many of them were close, but I can say with all certainty that no one in my family is close to each other. The competition wasn’t healthy, and frankly none of us were willing to sacrifice our own agenda for the common good. There was no unity, because each of us were scared that the other would benefit at our expense. Looking back, this was an understandable fear because parental attention and investment are finite resources. If any of us played too nice, we risked getting ignored and overlooked by overwhelmed parents. Selfishness was the name of the game, and if we didn’t fight for ourselves we would become roadkill, or so we thought. Fear of annihilation suppressed any instincts for community and altruism.

Now that I’m an adult and I can make decisions for myself, I have made the choice to adopt and live by different values. I’m not a smug asshole about it, I just don’t want to live like that anymore. And more than anything, I can’t be judgmental about it because I understand why all 8 of us–without exception, were a bunch of self-absorbed jackals. Back then, the consequences of not being selfish were just too devastating. The emotional isolation was a natural result from the toxic family dynamic. I’m not going to generalize, but I’d be willing to wager that some of us are born selfish on an instinctual level, consequences be damned. It’s this pervasive feeling that there’s only room for one, and you have to choose between saving yourself over someone else.

While this is just complete speculation, it is my belief that this zero sum dynamic is what triggers fetus in fetu, or parasitic twin syndrome. In cases like these, the pregnancy starts out with 2 or more zygotes. As the pregnancy progresses, one fetus in particular manages to hog all of mom’s resources, leaving none for the other fetus. Eventually, the starving fetus is absorbed by the dominant one. In some instances, the absorption is not complete, which means that the vestigial twin continues to live as a parasite inside the fully formed twin.

Half-Ass Fratricide in Utero?

A farmer in India, Sanju Bhagat, had been teased his whole life for “looking pregnant“. One day, he was rushed to the hospital for breathing problems. Doctors surmised that Bhagat was carrying a tumor in his stomach, which was pushing against his diaphragm and straining his breathing. When they operated on him, they discovered a parasitic twin instead–complete with hair, limbs, fingers, nails, and some rudimentary genitalia. There was no brain, but it was undeniably alive and could “shake your hand”.

A Woman’s Body Is Not A Clown Car

For better or for worse, the space and resources available inside a woman’s body is finite. Fetuses are not blind to this immutable fact. A uterus can only expand so much, only so much food can be eaten in one sitting. Given the circumstances, it’s easy to see how intrauterine sibling rivalry can lead to death and elimination for the weaker twin. It is estimated that fetus in fetu occurs once in every 500,000 live births–but that’s only counting births where the weaker twin manages to resist complete absorption and leaves proof of its existence, either as a parasite or a teratoma.

Fortunately, fetal selfishness isn’t always the rule–otherwise twins and triplets wouldn’t exist. Selfishness is a choice, a possibility you can make into a reality–but it’s not an inevitability. Nature isn’t always a battle royale, and in many circumstances the only way to survive and thrive is to cooperate and prioritize the interests of the community. In fact, our existence as multi-cellular organisms are possible only because of these principles. In the end, even the most selfish person understands that no man is an island–because in reality, the best way to promote your self interest is to care about other people’s self interest too.